The Self‐Ordering Properties of Novel Phthalocyanines with Out‐of‐Plane Alkyl Substituents

Abstract

Two novel homologous series of phthalocyanines were prepared from 2,2‐dialkylindane and 2,2‐dialkyl‐1,3‐benzodioxole precursors. It was anticipated that attaching alkyl chains to five‐membered rings, fused to the peripheral sites of the phthalocyanine ring, would result in the adoption of an out‐of‐plane configuration and thereby discourage cofacial aggregation, to provide an analogy with picket‐fence porphyrins. This strategy proved partially successful. Some members of the series of phthalocyanines derived from 2,2‐dialkyl‐1,3‐benzodioxoles, in which the alkyl chains are linked to the phthalocyanine via a cyclic ketal, form spin‐coated thin films in which the phthalocyanine cores are perfectly isolated. This behaviour is associated with the formation of a disordered crystal that appears as a mesophase in the thermal profile of these materials. However, the phthalocyanines derived from 2,2‐dialkylindanes display a columnar mesophase over a wide temperature range, with some liquid crystalline derivatives at ambient temperature. A single‐crystal X‐ray diffraction structure of the octahexyl derivative of this series shows how the columnar assembly accommodates the out‐of‐plane alkyl chains by tilting the macrocyclic plane of the phthalocyanine components with respect to the axis of the column. This study helps to emphasise the importance of both the steric and electronic effects of substituents on the packing behaviour of phthalocyanines in the condensed phase, and especially the role of electron‐donating oxygen atoms directly attached to the ring.

Long‐Range Self‐Assembly of an Electron‐Deficient Hexaazatrinaphthylene with Out‐of‐Plane Substituents

“…Nevertheless, longer length 2 C10 and 2 C12 upon cooling neither formed crystals or showed any birefringent, and small angle XRD diffractogram from cooling cycle did not show any prominent peaks, indicating a liquid‐like state. This observation was somewhat similar to the cyclic ketal phthalocyanine that had been reported to hamper the efficient π‐π stacking . Shearing of the cool sample did not lead to the mesophase formation .…”

“…described triphenylene‐based discotic liquid crystals . On the other hand, the out‐of‐plane cyclic ketal side chains of phthalocyanine core have been shown to form co‐facial columnar self‐association, despite the initial belief that the steric demand disfavor aggregation …”

Control over Nanostructures and Associated Mesomorphic Properties of Doped Self‐Assembled Triarylamine Liquid Crystals

“…This characteristic behavior of such triarylamines can be explained as a sort of aggregation‐induced emission (AIE),11g, 19 which is likely contributing by the restriction of intramolecular rotations in aggregates to lessen the non‐radiative decay of the photo‐excited states. The enhanced emission peaks are expected to appear in the higher wavelength region compared to the weak emission from the molecularly dissolved triarylamines (≈450 nm with structural bands corresponding to π–π* transitions4b, 20).…”

Tuning the Columnar Organization of Discotic Polycyclic Aromatic Hydrocarbons

“…The steric hindrance of the flexible side chains attached to the core is an effective tool for the solubility control, phase transition temperatures and the intracolumnar order. For linear alkyl side chains, a close relation between the number of carbon atoms in the substituent and the phase transition temperature or solubility was observed 32. For hexa‐substituted PAHs which possess a relatively large aromatic core in comparison to other discotics, dodecyl side chains ( 1b ) are necessary to disturb the strong π ‐stacking interactions and induce LC at accessible temperatures.…”